In a sense, the astronomical definition of winter has a lot more meaning in a connected world. I grew up in a part of Canada where the (colloquial) winter started at the end of October and ended at the end of March. I now live in a part of the country where it starts in late December and runs until the end of April. If you're trying to convey time by saying that something happened last winter, different people are going to have very different ideas of when that means.

Then again, perhaps we shouldn't be discussing time in terms of the seasons. Anyone in the southern hemisphere experiences the opposite, while people living in equatorial regions don't really share our notions of seasons (from my understanding).